In feed mycotoxins and swine performance

It is not a secret that animal feed containing mycotoxins are detrimental to swine production. Mycotoxins produced by certain strains of filamentous fungi such as Aspergillus, Penicillium and Fusarium,  are organic chemical compounds with a low molecular weight and a great stability with respect to pH conditions and temperature.

Mycotoxin contamination of feed is an ongoing global concern. Recent research shows that of all samples analysed, 70% were contaminated by more than one mycotoxin whereas 20% contained at least one mycotoxin. The simultaneous presence of multiple mycotoxins increases the toxicity to the animal. This leading to reductions in performance and/or health status that are often far higher than expected.

The toxic effects are determined by the ingested dose, the length of exposure, the interaction with other toxic substances and the genetic susceptibility of the individual. The affected organs are mainly those that are responsible for the metabolism (liver, kidneys and lungs), but they also effect the central nervous system, the immune system and the reproductive organs. Although in pig production acute clinical effects on the digestive and immune systems are especially important, we must not forget the importance of the subclinical effects which entail a continuous loss of production efficiency, genetic potential and profitability of the farm.

The problem of mycotoxins does not just end in animal feed or reduced animal performance; many become concentrated in meat of the animal and can pose a threat to human health.

Mycotoxins relevant in swine production

1. Aflatoxins
Aflatoxins (AF) B1, B2, G1 and G2, when present in  rations of swine are responsible for mycotoxicosis. .Aflatoxins are economically important as researchers estimate that for each ppm of aflatoxin in the feed, the growth rate of pigs is depressed by 16%.

Young swine are extremely sensitive to aflatoxins but susceptibility decreases with age. Apart from the age of the pig, the risk from aflatoxin-contaminated grain depends also on the health as well as the concentration of the toxin in the feed. Symptoms occur with concentrations in the parts per billion (ppb) range whereby the LD50 of aflatoxin for swine is very low (0.6mg/kg).  At low concentrations (20 to 200 ppb), chronic intoxication manifests by the decrease in weight gain and feed conversion, inappetence, poor general appearance and sometimes diarrhea.

High concentrations of aflatoxin (1.000 to 5.000 ppb) result in acute effects, including death. Clinical signs of acute aflatoxicosis may start 6 hours after ingestion, leading to severe depression, inappetence, blood in stools, muscle tremors, incoordination with hyperthermia and the death may occur in 12-24 hours following.
Sows that ingest AFB1 can eliminate aflatoxin M1 by milk, intoxicating piglets. Piglets from nursing sows consuming feed with 500 to 750ppb of aflatoxin had increased mortality and slower growth.

2. Ochratoxins
Ochratoxins are produced by fungi belonging to the genera Aspergillus and Penicillium  whereby Ochratoxin A (OTA), mainly a contaminant of cereal grains, is the most prevalent one.

Pigs are particularly sensitive to OTA because of its long serum half-time and tissue accumulation. The half-time of OTA in pig plasma is 20-30 times longer than that in poultry plasma, leading to a higher OTA contamination level and incidence in pigs.

Chronic exposure to lower levels of OTA causes a typical disease called porcine nephropathy (kidney damage). This can result in rejection of carcasses in the slaughter house.
Ochratoxin at concentrations greater than 5 to 10ppm in feed, results in a number of pathological conditions. These include impairment of kidney function, blood in the urine, enteritis, necrosis of lymph nodes and fatty liver changes.

OTA also  affects fertility of boars. It crosses the placenta barrier and can affect the development of foetuses. Tail necrosis sometimes observed in newborn piglets, is often associated with OTA.

3. Fumonisins
The Fumonisins (FUM), are a group of mycotoxins originally isolated from Fusarium moniliforme. Six different FUMS have been identified (A1, A2, B1, B2, B3, B4), however Fumonisin B1 (FB1) has been reported to be the most predominant one. The swine have a high sensitivity to fumonisins, supporting only concentrations below 10mg/kg food.

Like in most animals, in swine, fumonisin impairs immune function, causes liver and kidney damage, decreases weight gains and increases mortality rates. This immunosuppression is economically important as adverse effects on the immune system may lead to increased pathogen susceptibility and lowered vaccinal response.  Production parameters can also be affected: reduced weight gain (above 2ppm), increased FCR and reduced performances.

Signs of acute fumonisin intoxication include non-specific symptoms, such as hepatotoxicity and renal failure. Recently acute pulmonary edema (filling of the lungs with fluid) has been reported as a species specific symptom of fumonisin toxicity in pig whereby all ages of pigs have been reported to be affected. Mortality rates have been recorded in the range of 10% to 40%.

4. Tricothecenes
Tricothecenes (TCT) is a group of toxic fungal metabolites produced by a number of species of the genus Fusarium and can be divided into 2 groups.
- Group A tricothecenes including T-2 toxin, HT-2 toxin and diacetoxyscirpenol (DAS)
- Group B tricothecenes: deoxynivalenol (DON or vomitoxin), nivalenol ( NIV) and Fusarenon-X

Swine and other monogastric  animals show increased sensitivity to TCT whereby Deoxynivalenol and T-2 toxin appear as the most harmful TCT’s in pigs. Growth retardation, weight gain suppression and feed refusal is observed when pigs are chronically exposed to lower doses of DON (≥50µg/kg BW) and T-2 (≥10 µg/kg BW).

T-2 toxin and other type A TCT’s cause reduced productivity at feed concentrations of 200ppb or less. In sows, infertility with some lesions in the uteri and ovaries can be observed after a feed with 1 to 2 ppm of T-2toxin has been consumed. T-2 is one of the most acute toxic mycotoxins whereby mycotoxicosis in pigs is characterized by multiple hemorrhages on the serosa of the liver and along the intestinal tract.

DON at levels above 1ppm causes a disease called moldy corn toxicosis of swine making the grain unpalatable decreasing the feed intake. Above 5ppm, depression of feed intake may become severe and at 10 ppm, there will be a severe  feed refusal resulting in weight loss. At concentrations approaching 20ppm, vomiting may be observed in pigs within approximately 15 minutes of initial consumption.

In mature sows, DON causes failure in return to oestrus and reduced efficiency but also intestinal tract inflammation and acute diarrhea of suckling piglets, resulting in high mortality. Sows receiving a diet containing 2ppm of DON showed a decreased feed intake of 21% during the whole lactation period resulting in a reduced weight gain of the piglets in the contaminated group.

All TCT can be acutely lethal but the biggest problems tend to be subacute toxicosis reaching chronicity leading to nonspecific effects associated with poor performance.

5. Zearalenone
Zearalenone, also called ZON, Zea or Zen, is a non-steroidal estrogenic mycotoxin produced by Fusarium. Of all mycotoxins produced, zearalenone affects reproduction most seriously since it mimics the reproductive steroids of the estrogen family.   The specific manifestations of ZON in pigs are dependent on the dose, age, stage during oestrus cycle and pregnancy or not.
The prepuberal gilt is of all domestic species, the most sensitive to Zea with concentrations as low as 0.5 to 1 ppm causing pseudo-oestrus and vaginal or rectal prolapse. Higher concentrations can interfere with ovulation, conception, implantation and foetal development. However, results from several studies indicate that the estrogenic properties of Zea are not permanent and that gilts can successfully enter the breeding herd without a reduction in fertility after a 2-week withdrawal from zearalenone ingestion.

 In pregnant sows, it can increase the incidence of abortion and still births, reduce litter size and piglet viability. The lactating sows also is susceptible to Zea at high concentrations. Sows fed 50 to 100ppm  Zea for 2 weeks before weaning and for 63 days after weaning exhibit constant oestrus. Low concentrations (2 to 5 ppm) fed throughout pregnancy and lactation will not affect post weaning rebreeding.

Young boars may have reduced libido and decreased testicular size but mature boars are rarely affected. Mature boars receiving diets with 200ppm have  normal libido scores and normal sperm concentrations when compared with boars consuming a normal ration.

Next to their major effects on reproduction and the homone system, ZON and its metabolites may also effect other organ systems. It has shown to be hemotoxic. It disrupts the blood coagulation process, alters haematological parameters as well as some serum biochemical parameters such as aspartate aminotransferase, alanine aminotransferase, serum creatine and bilirubin.
More recent research data indicates ZON stimulates the growth of mamma tumors containing estrogen receptors, indicating it can play a role in tumor development after chronic exposure.

6. Ergot
Ergot are alkaloid toxins produced by rye ergot (Claviceps purpurea), which affects wheat, oats and ryegrass. They cause contraction of the walls of small blood vessels (capillaries), thereby restricting irrigation, particularly mammary gland and limbs. Diagnosis is difficult and is based on clinical condition, especially necrosis of the extremities.

The effects of ergot toxicity in are reduced growth performance and feed refusal has been associated with ergot-infected feed. Significant reproductive losses such as small litter sizes, premature farrowing, repeat oestrus, metritis and mastitis have been observed in sows consuming ergot alkaloids. Additionally, milk production is reduced or halted entirely in the presence of ergot due to the inhibition of prolactin production. The combination of agalactia and premature farrowing often results in the birth of smaller, weaker piglets who must be managed separately and generally do not meet expected performance measures.

The cost of mycotoxins in pig production

Several mycotoxins may be produced concomitantly in the same substrate. In addition, cross-contamination among raw ingredients in feed mills also contributes to increases in the incidence of combined mycotoxins in animal diets. Discussing interaction among mycotoxins, from a meta-analysis of publications (>100), Grenier and Oswald (2011) observed that a combination of mycotoxins, at concentrations that individually should not cause negative effects, may negatively affect animals.

The moment mycotoxins impact growth and other performance parameters, profitability gets also altered. Considering a vast portion of the grain productions is contaminated by mycotoxins, represent a major concern worldwide in the pig production chain, since the effect of these toxins is to reduce animal performance.
Through meta-analysis, using articles published between 1968 and 2010, totalling over 1000 treatment  and 13.196 animals, the association of mycotoxins with performance in growing pigs was studied.

Contamination of diets with individual mycotoxins reduced feed intake by 14% and weight gain by 17%.  Parallel, combined mycotoxins reduced the same parameters by 42% and 45% respectively in comparison with the control group. However, groups challenged by individual and combined mycotoxins showed a similar feed conversion ratio, possibly because feed intake and weight gain responses were influenced by mycotoxins to a similar magnitude within each challenge type.

From the mycotoxins tested, deoxynivalenol and aflatoxins are the mycotoxins with the greatest impact on the feed intake and growth of the pigs, reducing by 26% and 16% in the feed intake and by 26% and 22% in the weight gain.
The mycotoxin effect on growth was greater in the males compared with the effect on females. The reduction in weight gain was 19% in the male group, where in the female group, a reduction of 15% was seen.

Conclusion
Mycotoxins have an influence on performance in pigs.  Animals fed with diets containing mycotoxins showed a reduction in feed intake, weight gain, feed conversion ratio and final BW in relation to the control group. Preventing mould growth and subsequent mycotoxin production is essential to the feed manufacturer, livestock producer and for maximum animal performance.

Author:
Bart De Meue - freelance marketing
Commissioned by Sanluc International nv

References
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